It is well known that both analog and digital signals can be transmitted over an electronic data transmission system. It is also well known that analog and digital signals are fundamentally different. Despite their fundamental differences, however, analog and digital signals still have certain common characteristics. In particular, for signal transmission purposes, both digital and analog signals exhibit identifiable frequency characteristics which allow digital signals to be processed as analog signals. Specifically, for an essentially digital signal, the related frequency characteristic is its symbol rate (i.e. the rate at which signals, e.g. digits or state changes, are transmitted along a particular electronic connection).
In the context of electronic data transmission systems, and with specific concern for signal distortions which can be caused by frequency interference during a transmission, there are many applications which employ a low pass filter in order to improve the Signal-to-Noise-Ratio (SNR) of the signal. As the name implies, a low pass (analog) filter is one which freely passes signals of all frequencies (symbol rates) that are below a reference value (i.e. the cut-off frequency). Not surprisingly, many low pass filters require equalization (i.e. alteration or compensation) in order to efficiently and efficaciously perform their intended function in a data transmission system.
A specific filter response for reducing the bandwidth of a data input signal which is akin to a low pass filter in several respects, is provided by what is commonly referred to as a Nyquist filter. The advantage of a Nyquist filter is essentially two-fold. For one, in the time domain, a Nyquist filter provides optimal suppression of inter-symbol interference. Simultaneously, in the frequency domain, a Nyquist filter provides for effective adjacent channel rejection. Heretofore, however, Nyquist filters have required the implementation of relatively sophisticated software for their operations. Moreover, Nyquist filters typically employ Digital Signal Processing (DSP) techniques that make them impractical at high data rates. Also, certain types of Nyquist filters appear to be impractical due to poor time response characteristics. Despite these shortcomings, Nyquist filters have certain desirable attributes for processing analog signals.
With the above in mind, it is an object of the present invention to provide a system and method for achieving a transfer function for a data transmission system that approximates a Nyquist filter response. Another object of the present invention is to establish an architecture for a data transmission system which avoids Digital Signal Processing (DSP) to achieve a much higher operational speed for the system with less power. Still another object of the present invention is to provide a system and method for equalizing a low pass filter using relatively inexpensive hardware components, such as a low pass filter in combination with a tapped delay filter, to create a Nyquist filter response for a data transmission system. Another object of the present invention is to provide a system and method for equalizing a low pass filter to reject high frequency interference. Yet another object of the present invention is to provide a system and method for equalizing a low pass filter to create a Nyquist filter response in a data transmission system which is easy to implement, is simple to use, and is comparatively cost effective.